Memory device

ABSTRACT

A memory device includes a semiconductor column extending above a substrate, a first conductive layer on a first side of the semiconductor column, a second conductive layer on a second side of the semiconductor column, opposite to the first conductive layer, a third conductive layer above or below the first conductive layer and on the first side of the semiconductor column, a fourth conductive layer on the second side of the semiconductor column, opposite to the third conductive layer, and a bit line connected to the semiconductor column. During reading in which a positive voltage is applied to the bit line, first, second, third, and fourth voltages applied to the first, second, third, and fourth conductive layers, respectively, wherein the first voltage and the third voltage are higher than each of the second voltage and the fourth voltage, and the third voltage is higher than the first voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-051173, filed Mar. 15, 2016, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a memory device.

BACKGROUND

Generally, a memory device that includes memory cells arranged in threedimensions is known.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a memory device of anembodiment.

FIG. 2 is a diagram illustrating an example of a memory block of amemory device of a first embodiment.

FIG. 3 is a diagram schematically illustrating an example of a structureof a portion of a block of the first embodiment.

FIG. 4 is a diagram illustrating an example of details of a crosssection along the xz plane of the structure of FIG. 3.

FIG. 5 is a timing diagram of voltages of several wiring lines of aselected block of the memory device of the first embodiment duringreading.

FIG. 6 is a schematic diagram illustrating an example of voltages ofseveral wiring lines of the memory device of the first embodiment at apoint in time during reading.

FIG. 7 is a table illustrating an example of voltages of several wiringlines of the memory device of the first embodiment at a point in timeduring reading.

FIG. 8 is a diagram illustrating a state of a certain region of thememory device of the first embodiment during reading.

FIG. 9 is a diagram illustrating an equivalent circuit of a portion ofthe memory device of the first embodiment.

FIG. 10 is a timing diagram of voltages of several wiring lines of aselected block of the memory device of a modification example of thefirst embodiment during reading.

FIG. 11 is a timing diagram of voltages of several wiring lines of aselected block of a memory device of a second embodiment during reading.

FIG. 12 is a schematic diagram illustrating an example of voltages ofseveral wiring lines of the memory device of the second embodiment at apoint in time during reading.

FIG. 13 is a table illustrating an example of voltages of several wiringlines of the memory device of the second embodiment at a point in timeduring reading.

FIG. 14 is a diagram illustrating a state of a certain region of thememory device of the second embodiment during reading.

FIG. 15 is a diagram illustrating an equivalent circuit of a portion ofthe memory device of the second embodiment.

FIG. 16 is a table illustrating a first modification example of voltagesof the memory device of the second embodiment applied at a point in timeduring reading.

FIG. 17 is a timing diagram illustrating a second modification exampleof voltages of the memory device of the second embodiment applied at apoint in time during reading.

FIG. 18 is a timing diagram of voltages of several wiring lines of aselected block of a memory device of a third embodiment during writing.

FIG. 19 is a table illustrating an example of voltages of several wiringlines of the memory device of the third embodiment at a point in timeduring writing.

FIG. 20 is a timing diagram of voltages of several wiring lines of aselected block and an non-selected block of a memory device of a fourthembodiment during erasing.

FIG. 21 is a table illustrating an example of voltages of several wiringlines of the memory device of the fourth embodiment at a point in timeduring reading.

DETAILED DESCRIPTION

Embodiments provide a memory device capable of enhancing reliability.

According to an embodiment, a memory device includes a semiconductorcolumn extending above a substrate, a first conductive layer on a firstside of the semiconductor column, a second conductive layer on a secondside of the semiconductor column, opposite to the first conductivelayer, a third conductive layer above or below the first conductivelayer and on the first side of the semiconductor column, a fourthconductive layer on the second side of the semiconductor column,opposite to the third conductive layer, and a bit line connected to thesemiconductor column. During reading in which a positive voltage isapplied to the bit line, a first voltage is applied to the firstconductive layer and a second voltage is applied to the secondconductive layer, and a third voltage is applied to the third conductivelayer and a fourth voltage is applied to the fourth conductive layer,wherein the first voltage and the third voltage are higher than each ofthe second voltage and the fourth voltage, and the third voltage ishigher than the first voltage.

Hereinafter, description will be made on the present embodiment withreference to the accompanying drawings. In the following description,elements having substantially the same functionality and configurationare denoted by the same reference numerals and description thereof willnot be repeated. It should be noted that drawings are schematicallyillustrated and a relationship between a thickness and plane dimension,a ratio of thickness in each layer and the like are different fromactual ones. Embodiments herein are described in order to exemplify anapparatus or a method for embodying a technical spirit of theembodiments, and the technical spirit of the embodiments regardingmaterial of components, a shape, a structure, an arrangement, appliedvoltage, and the like are not limited to those described in thefollowing description.

Configuration and Structure

FIG. 1 is a functional block diagram of a memory device (semiconductormemory device) 100 of a first embodiment. As illustrated in FIG. 1, thememory device 100 includes elements such as a memory cell array 111, arow decoder 112, a sense amplifier 113, a sequencer (controller) 141, acharge pump 142, a driver 144, a logic control circuit 145, and aninput/output circuit 146.

The cell array 111 includes a plurality of memory blocks BLK (BLK0,BLK1, . . . ). The block BLK corresponds to, for example, a portionbetween contacts 45 (see FIG. 3), which will be described later, and forexample, is a unit of data erasure, and pieces of data in each block BLKare erased in a batch. Data may be erased in a unit (for example, onehalf of a block BLK) smaller than a single block BLK.

Each block BLK includes a plurality of string units (chunk) SU (SU0,SU1, . . . ). Each string unit SU includes a plurality of NAND stringsNS. The string NS includes a cell transistor MT (not illustrated). Thecell array 111 is further provided with wiring lines (not illustrated)such as a word line WL, a bit line BL, a source line SL, and selectiongate lines SGDL and SGSL.

The input/output circuit 146 transmits and receives signals I/O 0 to I/O7 to and from outside of the memory device 100. The signal I/O has, forexample, an 8-bit width, is a physical object of data, and includes acommand, write data or read data, and an address signal.

The logic control circuit 145 receives various control signals fromoutside of the memory device 100 and controls the sequencer 141 and theinput/output circuit 146 based on the control signals. The controlsignals include, for example, signals CEn, CLE, ALE, WEn, REn, WPn, andRY/BYn. The “n” added at the end of a signal name means that the signalis asserted in a case where a signal is at a low level.

The signal CEn which is asserted enables the memory device 100. Thesignals CLE and ALE which are asserted notify the memory device 100 thatsignals I/O, which flow to the memory device 100 together with theasserted signals CLE and ALE, are a command and an address,respectively. The signal WEn which is asserted instructs the memorydevice 100 to take in the signal I/O, which flow to the memory device100 together with the asserted signal WEn. The signal REn which isasserted instructs the memory device 100 to output the signal I/O. Thesignal WPn which is asserted gives an instruction prohibiting a datawrite and a data erasure to the memory device 100. The signal RY/BYnindicates whether the memory device 100 is in a ready state (a statebeing ready to receive instruction from outside of the memory device100), in a busy state (a state of not being ready to receive instructionfrom outside of the memory device 100), and the busy state is indicatedby the low level.

The sequencer 141 controls the charge pump 142, the row decoder 112, andthe sense amplifier 113 based on the command signal and the addresssignal.

The charge pump 142 receives a power supply voltage (potential) fromoutside of the memory device 100 and generates various voltages(potential) from the power supply voltage. The generated voltage issupplied to the driver 144 or the like. The voltage generated by thecharge pump 142 includes, for example, voltages to be applied to theword line WL, the selection gate lines SGDL and SGSL, and the sourceline SL. The driver 144 receives voltages generated by the charge pump142 and supplies a voltage selected from the received voltages to therow decoder 112 according to the control of the sequencer 141. The rowdecoder 112 receives various voltages from the driver 144, selects asingle block BLK based on the address signal from outside of the memorydevice 100, and transfers the voltage from the driver 144 to theselected block BLK. The sense amplifier 113 senses data read from thecell transistor MT and transfers write data from outside of the memorydevice 100 to the cell transistor MT.

The block BLK includes, for example, elements and connectionsillustrated in FIG. 2. As illustrated in FIG. 2, the block BLK includes,for example, four string units SU. Each string unit SU includes aplurality of strings NS as described above and is, for example, a set ofthe plurality of strings NS. In a case where an underscore and a numberfollowing the underscore are added at the end of a name of an element,the number following the underscore distinguishes among the sameelements.

Each string NS is connected between the source line SL and a single bitline BL. Each string NS includes cell transistors MT (MT0 to MTn), dummytransistors DST and DDT, and selection gate transistors SST and SDT. The“n” is a natural number. Each string NS may include a single dummytransistor or a plurality of dummy transistors between one of theselection gate transistors SST and SDT and the cell transistors MT. Eachstring NS may include the plurality of dummy transistors DST connectedin series and (or) the plurality of dummy transistors DDT connected inseries. The transistors SST, DST, MT0 to MTn, DDT, and SDT are connectedin series in this order. Each cell transistor MT may be stored in anonvolatile manner according to the quantity of charges contained in thelayer.

A control gate electrode of each cell transistor MTp (p is 0 or anatural number of n or less) of each string NS of each string unit SU isconnected to a word line WLp. Each word line WL is able to be controlledindependently by the row decoder 112. Each dummy transistor DST of eachstring NS of each string unit SU is connected to a word line WLDS (dummyword line). Each dummy transistor DDT of each string NS of each stringunit SU is connected to a word line WLDD (dummy word line). A gate ofeach selection gate transistor SDT of each string NS of each string unitSU is connected to the selection gate line SGDL. A gate of eachselection gate transistor SST of each string NS of each string unit SUis connected to the selection gate line SGSL. Furthermore, two stringunits SU, SU1 and SU2, which are adjacent to each other, share the sameword line WLs and the selection gate line SGSL.

In other embodiments, string units SU1 and SU2 may or may not share theselection gate line SGSL.

Each bit line BL is connected to the sense amplifier 113 (notillustrated).

The block BLK has a structure illustrated in FIG. 3, for example. FIG. 3schematically illustrates an example of a structure of a portion of ablock of the first embodiment. FIG. 4 is a diagram illustrating anexample of details a cross section along the xz plane of the structureof FIG. 3. In particular, FIG. 3 and FIG. 4 represent a portion relatedto four string units SU0 to SU3 within a single block BLK.

As illustrated in FIG. 3, the string units SU0 to SU3 are provided onthe semiconductor substrate 10. The string units SU0 to SU3 are alignedalong the x-axis. Each string unit SU includes the plurality of stringsNS aligned along the y-axis. Each string NS is connected to a p-typewell (CP well) 12 in the lower end and connected to one of the pluralityof conductive lines 33 through the conductive line 29 and vias (viaplugs) 31 in the upper end. The CP well 12 is provided in an n-type well11 and the well 11 is provided in a region on a surface of the substrate10. The well 11 and the CP well 12 extend along the xy plane. Theconductive lines 33 function as a bit line BL, extend along the x-axis,and are aligned along the y-axis.

The string NS includes a portion of a pillar (column) 15 containingsemiconductor materials. The transistors SST, DST, MT, DDT, and SDT areprovided along the pillar 15.

The pillar 15 is provided on the CP well 12. The pillar extends alongthe z-axis, is arranged in a matrix configuration along the xy plane,and includes a first portion 15 a. The first portion 15 a containssemiconductor materials, for example, silicon and is not doped withimpurities. The first portion 15 a functions as a side surface of thepillar 15 and has, for example, a cylindrical shape, and is in contactwith CP well 12 at the lower end. The pillar 15 includes a secondportion 15 b. The second portion 15 b corresponds to a portion where thefirst portion 15 a is not provided, that is, the inside portion of acylinder in a case where the first portion 15 a has a cylindrical shape.The second portion 15 b is a cavity, includes an insulator, or includesboth the cavity and the insulator. One side in the x-axis direction ofeach pillar 15 functions as a current path for the transistors SST, DST,MT, DDT, and SDT included in a single string NS. The other side in thex-axis direction of each pillar 15 functions as a current path for thetransistors SST, DST, MT, DDT, and SDT included in another string NS.

A tunnel insulating film 17 is provided on side surfaces of each pillar15. The tunnel insulating film 17 covers, for example, the side surfacesof the pillar 15. The tunnel insulating film 17 contains, for example,silicon oxide.

A plurality of films 19 are provided on a surface of the tunnelinsulating film 17 along the z-axis. The films 19 have a length alongthe z-axis (that is, a thickness), are aligned along the z-axis atintervals, have, for example, conductivity, function as a floating gateelectrode, and are referred to as a floating gate electrode film 19 inthe following. The floating gate electrode film 19 consists ofinsulating materials in one embodiment. A surface except for a portionof the surface, which is in contact with the tunnel insulating film 17of the floating gate electrode film 19, is covered with the insulatingfilm 21. The insulating film 21 contains, for example, silicon nitride.

A plurality of the conductive films 23 are provided to be opposed to aplurality of floating gate electrode films 19 in a one-to-onerelationship. The conductive film 23 functions as a control gateelectrode (word line WL, dummy word lines WLDD and WLDS, and selectiongate lines SGDL and SGSL), and is referred to as a control gateelectrode film 23 in the following. The control gate electrode film 23has a length along the z-axis (that is, a thickness), is aligned alongthe z-axis at intervals, is provided, for example, at a position havinga height (a position on the z-axis) which is equal to that of thefloating gate electrode film 19, and extends along the y-axis. Eachcontrol gate electrode film 23 faces all of strings NS of a singlestring unit SU. More specifically, each control gate electrode film 23faces the pillar 15 for each of all of strings NS of a single stringunit SU in one side.

Two edges of each control gate electrode film 23 that is between the twopillars 15 aligned and adjacent in the x-direction, are opposedrespectively to two floating gate electrode films 19 in contact with thetwo pillars 15. The uppermost control gate electrode film 23 (23 a) withregard to the z-axis does not face both of the two pillars 15 alignedand adjacent in the x-direction but faces only a single pillar 15.

The control gate electrode film 23 (word line WL, dummy word lines WLDDand WLDS, and selection gate lines SGDL and SGSL), has an end facing thepillar 15 with a shape of, for example, a semi-circular shape in crosssection, in the xy plane as illustrated in FIG. 6. Although notillustrated, for example, the floating gate electrode film 19 also has asimilar shape along an end of the word line WL in the xy plane, andsurrounds about half of the pillar 15.

Referring back to FIG. 3 and FIG. 4, a surface, which faces at least thefloating gate electrode film 19, of each control gate electrode film 23,is covered with an insulating film 25. The insulating film 25 contains,for example, silicon nitride, and covers, for example, the control gateelectrode film 23.

An insulating film 27 is provided between the insulating film 25 and theinsulating film 21. The insulating film 27 contains, for example,silicon oxide.

A set of elements in the region 31 functions as a stacked gate typetransistor. The transistor (hereinafter, referred to as a transistor 31)of the region 31 includes the single floating gate electrode film 19, aportion aligned with the floating gate electrode film 19 of the firstportion 15 a of the pillar 15, a portion aligned with the floating gateelectrode film 19 of the tunnel insulating film 17, the control gateelectrode film 23 facing the floating gate electrode film 19, and theinsulating films 21, 25, and 27 between the floating gate electrode film19 and the control gate electrode film 23. The gate of the transistor 31is the control gate electrode film 23, a channel region (a regionforming a channel of the transistor 31) is a portion of the firstportion 15 a of the pillar 15 facing the gate electrode film 23, thesource region and the drain region are both portions adjacent to thechannel region of the first portion 15 a of the pillar 15.

The nearest transistor to the substrate 10 functions as a selection gatetransistor SST and the farthest transistor from the substrate 10functions as selection gate transistor SDT, among the transistors 31using the same pillar 15. The conductive film 23 c of the selection gatetransistor SST functions as the selection gate line SGSL. The conductivefilm 23 a of the selection gate transistor SDT functions as theselection gate line SGDL, and may be referred to as the selection gateelectrode film 23 a or 23 c.

The transistor 31 adjacent to the selection gate transistor SST alongthe z-axis functions as the dummy transistor DST, among the plurality oftransistors 31 using the same the pillar 15. The transistor 31 adjacentto the selection gate transistor SDT along the z-axis functions as thedummy transistor DDT, among the plurality of transistors 31 using thesame the pillar 15.

The transistors other than the dummy transistors DST and DDT, and theselection gate transistors SST and SDT each function as the celltransistor MT, among the plurality of transistors 31 using the same thepillar 15. The cell transistor MT, as a result of writing, containselectrons injected through the tunnel insulating film 17 in the floatinggate electrode film 19 and stores data corresponding to the number ofelectrons. The cell transistor MT which is not holding data, that is,the cell transistor MT which is in a state where data are erased(erasure state), has a threshold voltage smaller than the thresholdvoltage of the cell transistor MT which is in a state where data arewritten.

The transistors SST, DST, MT, DDT, and SDT that use the same pillar 15and are aligned on the same side of the pillar 15 are connected inseries with each other through the first portion 15 a of the pillar 15.The transistors SST, DST, MT, DDT, and SDT connected in series with eachother through the first portion 15 a of the pillar 15 function as asingle string NS.

As described above, two strings NS aligned in the x-axis direction inthe string units SU1 and SU2 share the control gate electrode film 23.For that reason, the control gate electrode films 23 (except for thecontrol gate electrode film 23 a) of two strings NS aligned in thex-axis direction are connected with each other in the string units SU1and SU2.

A diffusion layer 37 doped with n-type impurities is provided in thesurface of the CP well 12 at a side of the pillar 15 for the stringunits SU0 and SU1 and opposite to the pillar 15 for the string units SU2and SU3. The diffusion layer 37 is connected to the lower end of thecontact 39. The contact 39 is connected to the conductive film 43 in theupper end through the contact 41. The conductive film 43 functions asthe source line SL. The conductive film 43 is also connected to theconductive film 50 by a contact (not illustrated). The conductive film50 is located above the conductive film 33 and extends, for example,along the xy plane, and functions as the source line SL.

A region between the control gate electrode films 23 is provided withthe insulating film 35.

The contact 45 is provided at a location spaced from the string unit SU3at a side of the string unit SU3, which is opposite to the string unitSU2. The contact 45 extends along the xy plane.

(Operation)

FIG. 5 is a timing diagram of voltages (potentials) of several wiringlines of a selected block of the memory device of the first embodimentduring reading. In one string unit SU, the word line WL and theselection gate lines SGSL and SGDL, and a voltage are shared among thestrings NS included therein. For that reason, in the following,description will be made using a single string NS of each string unit SUas representative.

In the memory device 100 having the structure illustrated in FIG. 3 andFIG. 4, four different states of voltage applications occur in thestring NS by selecting string NS and the word line WL. Four states ofthe string NS during a period between time t3 and time t4, which will bedescribed later, are illustrated in FIG. 6. FIG. 6 illustrates twopillars 15 that share a single bit line BL and a portion of elementsrelated to the pillars 15. Description for an element 40 illustrated inFIG. 6 will be made in a second embodiment.

The string NS1, which is in a first state, of four states of the stringsNS, is a selected string, and belong to a string unit SU1, for example.Second to fourth states occur in non-selected strings NS. The string NS0which is in the second state shares the pillar 15 with the selectedstring NS1. The string NS2 which is in the third state shares the wordline WL with the selected string NS1. The string NS3 which is in thefourth state does not share the pillar 15 and does not share the wordline WL with the selected string NS1, and belongs to the string unitSU3, for example. In the non-selected string NS2 which shares the wordline WL and the selection gate line SGSL with the selected string NS1,the wiring line to be shared is biased with a voltage which is the sameas that of the selected string NS1.

As illustrated in FIG. 5, at a time point time t0, all of word lines WL,all of selection gate lines SGSL and SGDL, the bit line BL, the sourceline SL, and the CP well 12 in any of the strings NS are controlled tohave a ground potential Vss (=0 V) by the control of the sequencer 141.

The sequencer 141 applies a voltage Vsg to the selection gate lines SGDL(SGDL_0 to SGDL_3) and SGSL (SGSL_0, SGSL_1, and SGSL_3) of all of thestrings NS temporarily from time t1. The voltage Vsg has a voltagemagnitude which is large enough to turn on the selection gatetransistors SDT and SST.

The sequencer 141 applies a voltage Vread to all of the word lines WLtemporarily from time t1. The voltage Vread has the voltage magnitudewhich is large enough to turn on any of the cell transistor MTregardless of its threshold voltage. The voltage application at time t1is performed to reset the pillar 15, that is, to dispel charges thatexist unintentionally in the pillar 15 from the pillar 15. However, thevoltage application at time t1 is optional in the embodiments.

The sequencer 141 maintains the voltage of the bit line BL at thevoltage Vbl from time t2 and maintains the voltage of the source line SLand the CP well 12 at the voltage Vcelsrc. The voltage Vbl and thevoltage Vcelsrc are each higher than the voltage Vss and the voltageVcelsrc is lower than the voltage Vbl. The application of the voltageVbl and the voltage Vcelsrc continues until time t4. Alternatively, thesequencer 141 may control the voltage of the bit line BL to be set toVcelsrc from time t2 and to Vbl from time t3, similar to thoseillustrated in FIG. 11 which will be described later.

From time t3, the sequencer 141 applies the voltage Vsg to the selectiongate line SGDL_1 and SGSL_1 of the selected string NS1. The voltage Vsgis applied to thereby turn on the selection gate transistors SDT_1 andSST_1. The application of the voltage Vsg continues until time t5.

On the other hand, the sequencer 141 continues to apply the voltage Vssto the selection gate lines SGDL_0, SGDL_2, SGDL_3, SGSL_0, and SGSL_3of the non-selected strings NS0, NS2, and NS3 from time t3 to time t5.For that reason, the selection gate transistors SDT_0, SDT_2, SDT_3,SST_0, SST_2, and SST_3 are maintained in an off state in thenon-selected strings NS0, NS2, and NS3.

The sequencer 141 applies the following voltages to the word lines WL0_1to WLn_1, WLDS_0, and WLDD_0 of the selected string NS1 from time t3 totime t5.

First, the sequencer 141 applies the voltage Vcgr to the word lineWLx_1, where “x” is 0 or a natural number of n or less. The word lineWLx_1 is connected to the cell transistor MT that is selected forreading (referred to as “selected cell transistor”) and is referred toas a selected word line in the following. The voltage Vcgr has avariable value based on the read data. The voltage Vcgr is applied suchthat the selected cell transistor MT having a threshold voltage, ofwhich magnitude is greater than or equal to the voltage Vcgr, maintainsan off state, and the selected cell transistor MT having a thresholdvoltage, of which magnitude is less than the voltage Vcgr, is turned on.

On the other hand, the sequencer 141 applies the voltage Vread to theword lines WL0_1 to WLx−2_1, WLx+2_1 to WLn_1, WLDS_1, and WLDD_1 andapplies the voltage Vreadk to the word lines WLx−1_1 and WLx+1_1. Thevoltage Vreadk is higher than the voltage Vread. Alternatively, thevoltage Vreadk may be equal to the voltage Vread.

The sequencer 141 applies the voltage Vneg to the word lines WL0_0 toWLn_0, WLDS_0, and WLDD_0 of the non-selected string NS0 and the wordlines WL0_3 to WLn_3, WLDS_3, and WLDD_3 of the non-selected string NS3from time t3. The voltage Vneg is smaller than a threshold voltage ofany of cell transistors MT that are in the erasure state, of the memorydevice 100. The voltage Vneg has a negative voltage value.

The voltage is applied at time t3 to thereby allow data maintained inthe selected cell transistor MT to be read into the sense amplifier 113.After data is read into the sense amplifier 113, the sequencer 141applies a voltage to reset the pillar 15 from time t5 to time t6. Thatis, the sequencer 141 applies the voltage Vsg to the selection gatelines SGDL_0, SGDL_2, SGDL_3, SGSL_0, and SGSL_3 of the non-selectedstrings NS0, NS2, and NS3, and applies the voltage Vread to the wordlines WLx_1, WLDD_0, WLDD_3, WLDS_0, WLDD_3, WL0_0 to WLn_0, and WL0_3to WLn_3. Resetting from time t5 to time t6 is, however, optional.Reading is ended at time t6.

The voltages applied to several wiring lines between time t3 and time t4are illustrated in FIG. 7 in a table format.

Reading is also performed during write (program) verification and duringerase verification. The write verification is performed afterapplication of a write voltage and indicates confirmation as to whetherdata is correctly written. The erase verification is performed afterapplication of an erase voltage and indicates confirmation as to whetherdata is correctly erased. The voltage Vneg in a case of reading duringthe erase verification has a value lower than the voltage Vneg in a caseof a normal reading and the write verification. Regarding other points,the reading during the erase verification and reading during the writeverification are the same as normal reading.

Thus, an example in which the string NS1 is selected is described. Acase where string NS0, NS2, or NS3 is selected is similar to the exampledescribed above. That is, the case where string NS0, NS2, or NS3 isselected is similar to the example in which the string NS1 is selected,except that the selection gate transistor SDT of the selected string NSis turned on and the selection gate transistors SDT of the remainingnon-selected strings NS are turned off. In a case where the string NS0is selected, the strings NS1, NS2, and NS3 are non-selected strings. Ina case where the string NS2 is selected, the strings NS0, NS1, and NS3are non-selected strings. In a case where the string NS3 is selected,the strings NS0, NS1, and NS2 are non-selected strings.

Advantages (Effects)

Each pillar 15 faces two independent control gate electrode films 23(word lines WL, WLDS, and WLDD) along different heights of the pillar15. Transistors are formed in portions of the pillar 15 which face twoof the respective word lines WL, WLDS, and WLDD, at each of thedifferent heights. The transistors are able to function as thetransistor MT and the transistors DST and DDT. The plurality oftransistors MT, DST, and DDT, which are positioned at different heightsand aligned on one side of the pillar 15, are electrically connectedthrough portions of the pillar 15 in which the transistors MT, DST, andDDT of the pillar 15 are aligned. Additionally, each pillar 15 faces twoindependent control gate electrode films 23 a (selection gate lineSGDL). With the structure described above, two independent strings NSare provided in each pillar 15. The two pillars 15 adjacent to eachother share the control gate electrode films 23 that are between them.The structure in which two independent strings NS are provided by asingle pillar 15 described above is referred to as a shared pillarstructure.

In the shared pillar structure, it is preferable that respective currentpaths of two strings NS that share a single pillar 15 are electricallyseparated from each other. That is, as illustrated in FIG. 8, a region15 a 1 facing the word line WLx_1 and a region 15 a 2 facing the wordline WLx_0 of the first portion 15 a of the pillar 15 need to beelectrically separated from each other. FIG. 8 illustrates a state in aboundary of the word lines WLx_0, WLX_1 of the strings NS0 and NS1 alongthe xy plane during reading of the memory device of the firstembodiment.

During reading, the voltage Vcgr is applied to the selected word lineWLx_1 in the selected string NS1. For that reason, it is considered thata positive voltage lower than the voltage Vcgr or the voltage Vss isapplied to the word line WLx_0 of the non-selected string NS0 and thus,a depletion layer DA is formed in a region 15 a 3 between the region 15a 1 and 15 a 2, and the regions 15 a 1 and 15 a 2 are electricallyseparated from each other by the depletion layer DA. That is, the region15 a 1 attains a voltage of which the value is close to the voltage Vcgrand the region 15 a 2 attains a voltage of which the value is close to apositive voltage or which is approximately the voltage Vss. As a result,the depletion layer DA is formed in the region 15 a 3 by a potentialdifference between the regions 15 a 1 and 15 a 2.

However, the regions 15 a 1 and 15 a 2 may be electrically connectedthrough the regions 15 a 3 a and 15 a 3 b by a parasitic transistorwhich is turned on by the voltage application to the word lines WLx_0and WLx_1. That is, a parasitic transistor PT1 a, in which the portionsfacing at the lower side of the region 15 a 1 and 15 a 2 respectivelyoperate as a drain (Da) and a source (Sa), a portion facing the region15 a 3 a of the word line WLx_1 operates as a gate Ga, a portion, whichis close to the word line WLx_1, of the region 15 a 3 a operates as thechannel region Cha, is formed. Similarly, a parasitic transistor PT1 b,in which the portions facing at the upper side of the region 15 a 1 and15 a 2 respectively operate as a drain (Db) and a source (Sb), aportion, which faces the region 15 a 3 b of the word line WLx_1,operates as a gate Gb, and a portion, which is close to the word lineWLx_1, of the region 15 a 3 b operates as the channel region Chb, isformed. A channel may be formed in the channel regions Cha and Chb bythe application of the voltage Vcgr to the word line WLx_1, and theregions 15 a 1 and 15 a 2, which are respectively for the strings NS1and NS0, may be electrically connected with each other. The selectedword line WLx_1 needs to receive the voltage Vcgr during reading andthus, the parasitic transistors PT1 a and PT1 b may be easily turned ondue to the effects of the selected word line WLx_1.

Therefore, a pair of the parasitic transistors PT may be formed betweenthe strings NS0 and NS1 as illustrated in FIG. 9. FIG. 9 illustrates anequivalent circuit of a portion of the memory device of the firstembodiment and also an equivalent circuit of the portion of FIG. 8. Theparasitic transistors PT1 a and PT1 b of FIG. 8 are drawn as a singletransistor PT1 in FIG. 9. A parasitic transistor PT2, which may beturned on during application of a positive voltage to the word lineWLx_0, is also formed between the strings NS0 and NS1.

When the parasitic transistor PT1 and/or parasitic transistor PT2 isturned on, the strings NS1 and NS0 are connected to each other.

Furthermore, in a case where the positive voltage or the voltage Vss isapplied to the word line WLx_0 of the non-selected string NS0 and thusthe threshold voltage is equal to or less than 0 V in a state where thecell transistor MTx_0 is in the erasure state, the cell transistor MTx_0may be turned on. As a result, regardless of the threshold voltage ofthe selected cell transistor MTx_1, the current flows in the celltransistor MTx_0 of the non-selected string NS0 but not in the selectedcell transistor MTx_1. This means that a current that does not correctlyreflect the state of the selected cell transistor MTx_1 flows. Inparticular, in a case where the selected cell transistor MTx_1 has thethreshold voltage higher than the voltage Vcgr (that is, an off state ismaintained by the application of the voltage Vcgr), a correct data readof the selected cell transistor MTx_0 is inhibited.

According to the first embodiment, the voltage Vneg is applied to theword line WLx_0 facing the selected word line WLx_1. The voltage Vneghas a negative voltage value. For that reason, it is difficult to turnon the parasitic transistor PT2. For that reason, the connection of thestrings NS0 and NS1 through the parasitic transistor PT2 is suppressedduring reading. Furthermore, the voltage Vneg is selected to be smallerthan a threshold voltage of any cell transistor MT, which is in an erasestate, of the memory device 100. Accordingly, the cell transistor MTx_0of the non-selected string NS0 is reliably turned off even when it is inthe erase state. For that reason, even if the strings NS0 and NS1 areelectrically connected to each other by the parasitic transistor PTbeing in an on state, formation of a current path through the celltransistor MTx_0 by bypassing the selected cell transistor MTx_1 issuppressed. This prevents an occurrence of a situation in which theselected cell transistor MTx_1 in the off state is erroneouslydetermined to be in an on state by the current flowing in the celltransistor MTx_0 of the non-selected string NS0.

According to the first embodiment, voltages indicated in the followingare applied to the control gate electrode films 23 and 23 a duringreading, in the memory device 100 having the shared pillar structure.That is, the voltage Vsg is applied to the selection gate lines SGDL andSGSL in the selected string NS1 and thus, a structure in which thetransistors MT, DST, and DDT are connected in series (in the following,may be referred to as a serially connected transistors) is electricallyconnected to the source line SL and the bit line BL. Additionally, inthe selected string NS1, the voltage Vcgr is applied to the selectedword line WLx and the voltage Vread or the voltage Vreadk is applied tothe remaining non-selected word line WL (WL0 to WLx−1 and WLx+1 to WLn)and the word lines WLDS and WLDD. For that reason, data are able to beread from the selected cell transistor MT_x in the selected string NS1.

The non-selected string NS2 shares the word lines WL, WLDS, and WLDDwith the selected string NS1 and thus, a state where data are able to beread from the selected cell transistor MTx is formed also in thenon-selected string NS2. However, the voltage Vss is applied to theselection gate line SGDL in the non-selected string NS2 and thus, theserially connected transistor is not connected to the bit line BL in thenon-selected string NS2. Accordingly, data of the selected celltransistor MTx of the selected string NS1 and data of the selected celltransistor MTx of the selected string NS2 are not read into a common bitline BL.

The potential Vss is applied to both the selection gate lines SGDL andSGSL in the non-selected strings NS0 and NS3. The serially connectedtransistors are not connected to the source line SL and the bit line BLin the non-selected strings NS0 and NS2.

Furthermore, the voltage Vneg is able to be applied to all of the wordlines WL, WLDS, and WLDD in the non-selected string NS0. Thus, all ofthe transistors MT, DST, and DDT of the non-selected string NS0 areturned off. The hindering of an accurate reading from the selectedstring NS1 due to the current path formed in the non-selected string NS0side of the pillar 15 is further suppressed.

Furthermore, the voltage Vneg is applied to all of the word lines WL,WLDS, and WLDD also in the non-selected string NS3. For that reason, allof the transistors MT, DST, and DDT are turned off also in thenon-selected string NS3. For that reason, in the pillar 15 shared by thenon-selected strings NS2 and NS3, the current path is formed in theportion of the non-selected string NS2 side by the cell transistors MT,DST, and DDT, but, the current path is not formed in the non-selectedstring NS3 side.

By the principle described above, only the data of the selected celltransistor MTx of the selected string NS1 are able to be read into thebit line BL.

Modification Example

According to a modification, the voltages are applied as illustrated inFIG. 10 during reading. FIG. 10 is a timing diagram of voltages ofseveral wiring lines of a selected block of the memory device of amodification example of the first embodiment during reading. In thefollowing, description will be made on the points different from thoseof FIG. 5.

As illustrated in FIG. 10, the sequencer 141 applies the voltage Vsg tothe selection gate line SGDL_1 from time t1 to time t6. The sequencer141 applies the voltage Vsg to the selection gate lines SGSL_0, SGSL_1,and SGSL_3 from time t1 to time t6. As a result, the serially connectedtransistors of the selected string NS1 are connected to the bit line BLand the source line SL over a period of time from time t1 to time t6.

The sequencer 141 applies the voltage Vsg to the selection gate lineSGDL_2 of the non-selected string NS2 from time t1 to time t3. As aresult, the serially connected transistors of the non-selected stringNS2 are connected to the bit line BL and the source line SL over aperiod of time from time t1 to time t3.

On the other hand, the sequencer 141 maintains the application of thevoltage Vss to the selection gate lines SGDL0_0 and SGDL_3 of thenon-selected strings NS0 and NS3 even at time t1. For that reason, theserially connected transistors of the non-selected strings NS0 and NS3are separated from the source line SL. The application of the voltageVss continues until time t5.

Furthermore, the sequencer 141, from time t1 to time t6, applies thevoltage Vread to the word lines WL0_1 to WLx−2_1, WLx+2_1 to WLn_1,WLDS_1, and WLDD_1 of the selected string NS1 and applies the voltageVreadk to the word lines WLx−1_1 and WLx+1_1.

By the application of the voltages from time t1 as described above, allof the transistors MT, SST, SDT, SST, and SDT of the selected string NS1and the non-selected string NS2 are turned on and the channels of thetransistors MT, SST, SDT, SST, and SDT are connected to the bit line BLand the source line SL, from time t1 to time t3.

The sequencer 141 applies the voltage Vcelsrc to the bit line BL fromtime t2. As a result, the voltage Vcelsrc is transferred to the channelsof all of the transistors MT, SST, SDT, SST, and SDT of the selectedstring NS1 and the non-selected string NS2.

The sequencer 141 applies the voltage Vbl to the bit line BL from timet3. The voltage application except for the voltage application to thebit line BL from time t3 is the same as that illustrated in FIG. 5.

According to the modification example, prior to application of a voltagefor an actual reading from time t3, the channels of all of transistorMT, SST, SDT, SST, and SDT are connected to the bit line BL and thesource line SL in the selected string NS1 and the non-selected stringNS2 which shares the control gate electrode film 23 except for thecontrol gate electrode film 23 a. In this state, the voltage Vcelsrc isapplied to bit line BL and the source line SL and thus, the channels ofall of the transistors MT, SST, SDT, SST, and SDT of the non-selectedstring NS2 are charged toward the voltage Vcelsrc through the transferof the voltage Vsg. This makes it possible to remove the charges thatexist unintentionally in the channels and suppress an erroneousoperation in the string NS1 and an erroneous reading due to the chargesthat exist unintentionally.

Second Embodiment

A memory device of the second embodiment includes the same functionalblocks as those of the first embodiment. On the other hand, in thesecond embodiment, the sequencer 141 is configured to perform operationsdescribed in the following. In the second embodiment, description willbe made on the points different from those of the first embodiment.

FIG. 11 is a timing diagram of voltages of several wiring lines of aselected block of the memory device of a second embodiment duringreading. Also, in the second embodiment, four different states ofvoltage applications occur in the string NS (string unit SU) similar tothe first embodiment. Four states of the string NS during a periodbetween time t3 and time t4, which will be described later, areillustrated in FIG. 12. FIG. 12 illustrates two pillars 15 that share asingle bit line BL and a portion of elements related to the pillar 15.

As illustrated in FIG. 11, the sequencer 141 applies the voltage Vm,instead of the voltage Vneg in the first embodiment, to the word lineWLx−1_0, WLx+1_0, WLx−1_3, and WLx+1_3, that face at least the wordlines WLx−1_1 and WLx+1_1 of the selected string NS1 along the xy plane,from time t3 to time t5. The voltage Vm is greater than the voltage Vnegand is less than the voltage Vread, and has, for example, a positivevoltage value. In a case where five or more strings NS are provided in asingle block BLK, the voltage Vneg or the voltage Vm may be applied tothe word lines WLx+1 and WLx−1 of the non-selected string NS other thanthe non-selected strings NS0 and NS3.

The voltages applied to several wiring lines between time t3 and time t4are illustrated in FIG. 13 in a table format.

Advantages (Effects)

When the voltage is applied according to the first embodiment, a largepotential difference is generated in the region 40 of FIG. 6. Asdescribed in the first embodiment, it is expected that the regions 15 a1 and 15 a 2 are electrically isolated from each other, during reading,due to the depletion layer DA of the region 15 a 3. However, asillustrated in FIG. 14, a potential difference between the regions 15 a1 and 15 a 2 is not able to be maintained due to the depletion layer DAand a leakage current may flow between the regions 15 a 1 and 15 a 2(for example, band-to-band tunneling current) depending on a combinationof a size of the pillar 15, a value of the voltage Vreadk, and a valueof the voltage Vneg. FIG. 14 illustrates a state in a boundary of theword line WLx+1_0 of the strings NS0 and NS1 in the region 40 along thexy plane during reading of the memory device of the second embodiment.Flowing of the leakage current may result in inability to maintain thepotential of the word line WLx+1_1 to the Vreadk and may cause anerroneous reading from the selected string NS1.

The high potential difference in the pillar 15 caused by the voltageVreadk and the voltage Vneg may also be generated between the word linesWLx+1_1 and WLx+1_3. The high potential difference caused by the voltageVreadk and the voltage Vneg may also be generated between the word linesWLx−1_0 and WLx−1_1. Furthermore, the high potential difference causedby the voltage Vreadk and the voltage Vneg may also be generated betweenthe word lines WLx−1_1 and WLx−1_3.

According to the second embodiment, in the memory device 100, duringreading, the voltage Vm is applied to portions of the word lines WL(WLx−1 and WLx+1) which are adjacent to the selected word line WLx. Thevoltage Vm is higher than the voltage Vneg and thus, the potentialdifference between the regions 15 a 1 and 15 a 2 is small and is atleast smaller than that of the first embodiment even when the word lineWL adjacent to the selected word line WLx receives the voltage Vreadk.For that reason, a potential difference of a portion where the largestpotential difference is generated (a portion illustrated in the region40) is reduced in the pillar 15 and unintentional flowing of tunnelingcurrent in the portion can be suppressed. Thus, erroneous reading of thememory device 100 can be further suppressed.

However, the parasitic transistor PT can be turned on by the applicationof the voltage Vm. FIG. 15 illustrates an equivalent circuit of aportion of the memory device 100 during reading. As illustrated in FIG.15, by the combination of the same elements as those described withreference to FIG. 9, the parasitic transistor PT4 which uses the wordline WLx+1_0 as a gate is formed between the strings NS0 and NS1 andformed between the strings NS2 and NS3. The parasitic transistor PT4 isturned on to thereby make it possible to electrically connect twocurrent paths (regions 15 a 1 and 15 a 2) in each pillar 15.

However, the word line WLx_0, which is parallel with the word line WLx,in the non-selected strings NS (for example, NS0 and NS3) receives thevoltage Vneg so that the transistor MTx_0 is turned off. For thatreason, for example, even though two current paths are electricallyconnected, a piece of information maintained by the selected celltransistor MTx_1 is correctly reflected in the read current. That is,the piece of information maintained by the selected cell transistorMTx_1 is able to be correctly read.

In order to further make the potential difference in the region 40smaller, the voltage Vm preferably has a voltage value which causes thedifference between the voltage Vm and the voltage Vreadk to be smaller.On the other hand, the voltage Vm preferably has a voltage value whichcauses the difference between the voltage Vm and the voltage Vneg to besufficiently small. This is for suppressing the current flowing in theparasitic transistor PT4 and maintaining a breakdown voltage between theword line WL receiving the voltage Vm and the word line WL receiving thevoltage Vneg. In the second embodiment, the voltage Vm has a voltagevalue capable of maintaining the breakdown voltage between two wordlines WL receiving the voltage Vm and the voltage Vreadk and thebreakdown voltage between the two word lines WL receiving the voltage Vmand the voltage Vneg. Thus, the memory device 100 is able to be operatedmore normally.

Modification Example

The charges illustrated in FIG. 16 may be applied to the non-selectedstrings NS0 and NS3 between time t3 and time t4. FIG. 16 illustrates afirst modification example of voltages of the memory device of thesecond embodiment applied at a certain point in time during reading.

As illustrated in FIG. 16, the sequencer 141 applies a voltage Vm2 tothe remaining word lines WLs, that is, the word lines WL0 to WLx−2, andWLx+2 to WLn, other than the word lines WLx−1, WLx, and WLx+1, in thenon-selected strings NS0 and NS3. The voltage Vm2 is larger than thevoltage Vneg and is smaller than the voltage Vm, and has, for example, apositive voltage value. The voltage is applied such that the potentialdifference between the word lines WL0 to WLx−2 and WLx+2 to WLn and theword lines WL0 to WLx−2 and WLx+2 to WLn corresponding to the selectedstring NS1 is Vread−Vm2 in the non-selected strings NS0 and NS3. As aresult, the potential difference between each pair of the word lines WLis smaller than those of FIG. 12 to FIG. 14 and flowing of tunnelingcurrent is prevented without maintaining the required potentialdifference, by the same principle as that described with reference toFIG. 15.

The dummy word lines WLDS_0, WLDD_0, WLDS_3, and/or WLDS_3 may receive avoltage Vm2 from the sequencer 141. Accordingly, it is possible toreduce a potential difference between dummy word lines WLDS of separatestrings NS and/or another potential difference between dummy word linesWLDS of separate strings NS.

Furthermore, as illustrated in FIG. 17, the same voltage application asthat of FIG. 11 may be applied to the second embodiment. FIG. 17 is atiming diagram of voltages of several wiring lines of a selected blockof the memory device of a second modification example of the secondembodiment during reading. In the following, description will be made onthe points different from those of FIG. 12.

As illustrated in FIG. 17, the sequencer 141 applies the voltage Vsg tothe selection gate line SGDL_1 from time t1 to time t6. The sequencer141 applies the voltage Vsg to all of the selection gate lines SGSL_0,SGSL_1, and SGSL_3 from time t1 to time t6.

The sequencer 141 applies the voltage Vsg to the selection gate lineSGDL_2 of the non-selected string NS2 from time t1 to time t3. On theother hand, the sequencer 141 maintains the application of the voltageVss to the selection gate lines SGDL0_0 and SGDL_3 of the non-selectedstrings NS0 and NS3 even at time t1. The application of the voltage Vsscontinues until time t5.

Furthermore, the sequencer 141 applies the voltage Vread to the wordlines WL0_1 to WLx−2_1, WLx+2_1 to WLn_1, WLDS_1, and WLDD_1 of theselected string NS1 and applies the voltage Vreadk to the word linesWLx−1_1 and WLx+1_1 from time t1 to time t6.

The sequencer 141 applies the voltage Vcelsrc to the bit line BL fromtime t2. The sequencer 141 applies the voltage Vbl to the bit line BLfrom time t3.

According to the second modification example, an advantage of acombination of the modification example of the first embodiment and thesecond embodiment may be obtained.

Third Embodiment

The third embodiment is related to writing in the memory device 100.

FIG. 18 is a timing diagram of potentials of several wiring lines of aselected block of the memory device of the third embodiment duringwriting. Similar to the first embodiment and the second embodiment, inthe following, description will be made using a single string NS of eachstring unit SU as a representative and operations described occur inparallel in the plurality of strings NS. Similar to the firstembodiment, the string NS1 is a selected string to be written. The wordline WLx, that is, the word line WLx_1 is a selected word line.

As illustrated in FIG. 18, the sequencer 141 applies the voltage Vss toall of wiring lines at a time point time t10.

The sequencer 141 applies the voltage Vsg to the selection gate lineSGDL_1 of the selected string NS1 from time t11. As a result, theselection gate transistor SDT_1 is turned on and serially connectedtransistors (a set of transistors MT, DST, and DST) are connected to thebit line BL in the selected string NS1. On the other hand, the sequencer141 continues to apply the voltage Vss to the selection gate linesSGDL_0, SGDL_2, and SGDL_3 of the non-selected strings NS0, NS2, andNS3. For that reason, the serially connected transistors are maintainedin a state of being disconnected from the bit line BL in thenon-selected strings NS0, NS2, and NS3.

The sequencer 141 applies the voltage Vsgs to all of selection gatelines SGSL_0 to SGSL_3 from time t11. The voltage Vsgs is larger thanthe voltage Vss and has a voltage magnitude which is not large enough toturn on the selection gate transistor SST. For that reason, the seriallyconnected transistors are not connected to the source line SL in any ofall selected strings NS. Accordingly, in the selected string NS1, theserially connected transistors are in a state of being connected to thebit line BL and in the non-selected strings NS0, NS2, and NS3, theserially connected transistors are not connected to the bit line BL aswell as the source line SL and are electrically floating.

The sequencer 141 applies the voltage Vdd to the source line SL fromtime t12. The sequencer 141 continues to apply the voltage Vss to thebit line (a writable bit line) BL connected to the selected string (awritable selected string) NS1 which includes the selected celltransistor MT which injects electrons into the floating gate electrodefilm 19 by writing. On the other hand, the sequencer 141 continues toapply the voltage Vdd to the bit line (a writing prohibition bit line)BL connected to the selected string (a writing-prohibited selectedstring) NS1 which includes the selected cell transistor MT which doesnot inject electrons into the floating gate electrode film 19 bywriting, from time t12.

The sequencer 141 applies the voltage Vgp to the word lines WLDD_0 toWLDD_3 and WLDS_0 to WLDS_3 of all of the strings NS from time t13. Thevoltage Vgp is higher than the voltage Vss and has a voltage magnitudewhich is large enough to turn on the transistors WLDD and WLDS.

The sequencer 141 applies the voltage Vpass to the non-selected wordlines WL0_0 to WLx−1_0, WL0_1 to WLx−1_1, WL0_2 to WLx−1_2, WL0_3 toWLx−1_3, WLx+1_0 to WLn_0, WLx+1_1 to WLn_1, WLx+1_2 to WLn_2, andWLx+1_3 to WLn_3 of all of the strings NS from time t13. The voltageVpass is small enough to be able to suppress erroneous writing into thenon-selected cell transistor MTi (i≠x) in the selected string NS1 and islarge enough to be able to increase the channels, to the extent that anincrease of a threshold voltage of the cell transistor MTx can besuppressed, by coupling in the selected string NS2 sharing the wordlines with the selected string NS.

The sequencer 141 also applies the voltage Vpass to the selected wordline WLx_1 of the selected string NS1 from time t13. Furthermore, thesequencer 141 also applies the voltage Vpass to the word lines WLx_0 andWLx_3 facing the selected word line WLx_1 of the non-selected stringsNS0 and NS3 from time t13 by coupling.

All of the transistors MT, DDT, and SDT are turned on in the selectedstring NS1 by the application of the voltage Vpass from time t13. Thechannels of the non-selected strings NS0, NS2, and NS3 are electricallyfloating and thus, the potentials of the channels of the non-selectedstrings NS0, NS2, and NS3 are increased by the application of thevoltage Vpass to be electrically floating.

The sequencer 141 applies the voltage Vsgd to the selection gate lineSGDL_1 of the selected string NS1 from time t14. The voltage Vsgd issmaller than the voltage Vsg. The voltage Vsgd has a voltage magnitudewhich is large enough to turn off the selection gate transistor SDT_1 ofthe writing-prohibited selected string NS1 while maintaining theselection gate transistor SDT_1 of the writable selected string NS1 inan on state. The selection gate transistor SDT_1 of the writableselected string NS1 is maintained in an on state by the application ofthe voltage Vsgd. As a result, the channel of the writable selectedstring NS1 continues to be connected to the bit line BL and maintains astate where the voltage Vss is applied. On the other hand, the selectiongate transistor SDT_1 of the writing-prohibited selected string NS1 isturned off by the application of the voltage Vsgd. As a result, thechannels of the writing-prohibited selected string NS1 is disconnectedfrom the bit line BL to be electrically floating.

The sequencer 141 applies the voltage Vpgm to the selected word lineWLx_1 of the selected string NS1 from time t15. The voltage Vpgm ishigher than the voltage Vpass. A large potential difference, due to thevoltage Vpgm and the voltage Vss, is formed between the selected wordline WLx_1 and the channel by the application of the voltage Vpgm in thewritable selected string NS1. As a result, electrons are injected intothe floating gate electrode film 19 of the selected cell transistorMTx_1 of the selected string NS1 connected to the writable bit line BL.

On the other hand, the sequencer 141 continues to apply the voltageVpass to non-selected word lines WL0_1 to WLx−1_1 and WLx+1_1 to WLn_1of the selected string NS1 even from time t15. The voltage Vpass issufficiently smaller than the voltage Vpgm. For that reason, thepotential difference formed between the non-selected word lines WL0 toWLx−1 and WLx+1 to WLn and the channels by the voltage Vpass and thevoltage Vss is sufficiently smaller than the difference between thevoltage Vpgm and the voltage Vss even in the writable selected stringNS1. For that reason, electrons are not injected into the floating gateelectrode film 19, writing is suppressed, or writing does not occur inthe non-selected cell transistors MT0 to MTx−1 and MTx+1 to MTn of thewritable selected string NS1.

Writing into the cell transistor MT0 to MTn is suppressed or writingdoes not occur in the writing-prohibited selected string NS1 even by theapplication of the voltage Vpgm. This is because the writing-prohibitedselected string NS1 is electrically floating, the channels are coupledwith the word lines WL0_1 to WLn_1, the potentials of channels areincreased by the application of the voltage Vpgm and the voltage Vpassto the word lines WL0_1 to WLn_1, and a small potential difference isonly formed between the word lines WL0_1 to WLn_1 and the channels. Thevoltage Vpass is set in such a way that even if the cell transistor MTxof the writing-prohibited selected string NS1 receives the voltage Vpgmin a gate, the channel of the writing-prohibited selected string NS1 hasa potential to suppress the writing.

The state of the non-selected string NS2 from time t15 is the same asthat of the writing-prohibited selected string NS1. Specifically, thepotential of the channel of the non-selected string NS2 is increased bycoupling and there is only a small potential difference between the wordlines WL0_1 to WLn_1 and the channel. For that reason, writing into thecell transistor MT0 to MTn is suppressed or writing does not occur, evenby the application of the voltage Vpgm, in the non-selected string NS2.

Furthermore, the sequencer 141 continues to apply the voltage Vpass tothe word line WLx_0 and WLx_3 of the non-selected strings NS0 and NS3even from time t15. Even at time t15, the non-selected strings NS0 andNS3 are also electrically floating. For that reason, even from time t15,the channels of the non-selected strings NS0 and NS3 maintain a state ofbeing increased to a value close to the voltage Vpass by the couplingwith the word lines WL0_0 to WLn_0 and WL0_3 to WLn_3, and there is onlya small potential difference between the word lines WL0_0 to WLn_0 andWL0_3 to WLn_3. Accordingly, writing into the cell transistors MT0 toMTn is suppressed or writing does not occur even in the non-selectedstrings NS0 and NS3.

Writing due to injection of electrons is performed by the voltageapplication from time t15 to time t16. The sequencer 141 returns thevoltage, which is applied to the selected word line WLx_1, to thevoltage Vpass from time t16.

The sequencer 141 returns the voltage applied to the writing prohibitionbit line BL and the source line SL to the voltage Vss from time t17. Thesequencer 141 decreases the voltage applied to the selection gate lineSGDL_1 of the selected string NS1 toward the voltage Vss from time t17.The sequencer 141 temporarily increases the voltage of the selectiongate line SGDL of the non-selected strings NS0, NS2, and NS3 and thevoltage of the selection gate lines SGSL of all the strings NS from timet17.

The sequencer 141 returns the voltage of the selection gate line SGDL ofthe non-selected strings NS0, NS2, and NS3, the voltage of the selectiongate lines SGSL of all of the strings NS, and the voltage of all theword lines WL of all the strings NS to the voltage Vss from time t18,and ends writing.

The potential applied to several wiring lines between time t15 and timet16 are illustrated in FIG. 19 in a table format.

Advantages (Effects)

According to the third embodiment, in the memory device 100 having theshared pillar structure, during writing, the voltage Vss is applied tothe selection gate lines SGDL and SGSL of the non-selected strings NS0,NS2, and NS3. For that reason, the non-selected string NS iselectrically floating. On the other hand, while the voltage Vss isapplied to the writable bit line BL and the voltage Vdd is applied tothe writing prohibition bit line BL, the voltage Vsgd and the voltageVsgs are applied to the selection gate lines SGDL and SGSL of theselected string NS1. For that reason, the writing-prohibited selectedstring NS1 is electrically floating and the writable selected string NS1continues to be connected to the bit line BL. Thus, the non-selectedstring NS and the writing-prohibited selected string NS1 areelectrically floating and the writable selected string NS1 is connectedto bit line BL.

In the selected string NS1, the voltage Vgp is applied to the word linesWLDD and WLDS, the voltage Vpgm is applied to the selected word line WL,and the voltage Vpass is applied to the non-selected word line WL whilethe writable selected string NS1 is connected to the bit line BL. Forthat reason, only the small potential difference is formed between theword line WL and the channel in the non-selected cell transistor MT ofthe writable selected string NS1. On the other hand, a large potentialdifference is formed between the word line WL and the channel in theselected cell transistor MT of the writable selected string NS1. Writingoccurs in the selected cell transistor MT of the writable selectedstring NS1, and writing is suppressed or writing does not occur in thenon-selected transistor MT of the writable selected string NS.

In the selected string NS1, the voltage Vgp is applied to the word linesWLDD and WLDS, the voltage Vpgm is applied to the selected word line WL,and the voltage Vpass is applied to the non-selected word line WL whilethe writing-prohibited selected string NS1 is electrically floating. Forthat reason, only the small potential difference is formed between theword line WL and the channel in the cell transistor MT of thewriting-prohibited selected string NS1. Thus, writing is suppressed or,writing does not occur in the cell transistor MT of thewriting-prohibited selected string NS1.

Furthermore, in the non-selected string NS, the voltage Vgp is appliedto the word lines WLDD and WLDS and the voltage Vpass is applied to allthe word lines WL while the non-selected string NS is electricallyfloating. For that reason, only the small potential difference is formedbetween the word line WL and the channel and writing into the celltransistor MT is suppressed or the writing does not occur in thenon-selected string NS.

As such, writing occurs in the selected transistor MT of the writableselected string NS1, and writing is suppressed or writing does not occurin the non-selected transistor MT of the writable selected string NS1,the writing-prohibited selected string NS1, and the non-selected stringNS. That is, in the memory device 100 having the shared pillarstructure, writing is able to be selectively performed into the selectedtransistor MT, which is subjected to be writing, of the selected stringNS.

Fourth Embodiment

The fourth embodiment is related to erasure in the memory device 100.

FIG. 20 is a timing diagram of potentials of several wiring lines of aselected block and an non-selected block of the memory device of thefourth embodiment during erasing. Similar to the first embodiment, inthe following, description will be made using a single string NS of aselected block BLK as a representative and operations described occur inparallel in all of strings NS of the selected block BLK. The erasurewill be described with reference to FIG. 3 and FIG. 21.

As illustrated in FIG. 20, at a time point time t20, the sequencer 141applies the voltage Vss to all of wiring lines.

The sequencer 141 makes the bit line BL, the selection gate lines SGDL_0to SGDL_3, and all of the word lines WL of the non-selected block intoan electrically floating state from time t21. The sequencer 141 appliesthe voltage Vera to the CP well 12 from time t21. The voltage Vera ishigher than the voltage Vss. The voltage of the CP well 12 istransferred to the first portion 15 a of the pillar 15 from the lowerend along the z-axis (an end of selection gate transistor SST side). Asa result, a bottom portion of the first portion 15 a (body of transistorMT) of the pillar 15 is increased to a voltage (≈Vera) close to avoltage value of the voltage Vera.

Furthermore, the sequencer 141 applies the voltage Vera−the voltageVerasgs to all selection gate lines SGSL_0 to SGSL_3 from time t21. Thevoltage Verasgs is a potential difference between the body 15 a of theselection gate transistor SST in a state of being in a chargeaccumulation state and selection gate line SGSL receiving the voltageVera−the voltage Verasgs, in other words, has a small voltage valueenough to make the body 15 a of the selection gate transistor SST intothe charge accumulation state. It becomes easy for the voltage of the CPwell 12 to be transferred to the upper portion of the body 15 a throughthe selection gate transistor SST by the application of the voltageVera−the voltage Verasgs.

The voltage Vera is applied to the CP well 12 and thus the voltage Veraof the CP well 12 is applied to the selection gate transistor SST in thebody 15 a. As a result, a bias voltage is applied from the body 15 a tothe diffusion layer 37 (a portion of source line SL) in a forwarddirection. For that reason, the voltage of the body 15 a is transferredto the conductive films 39 and 50 (source line SL) and the source lineSL is increased from the voltage Vss to a voltage value (≈Vera) close tothe voltage Vera.

The conductive films 43 and 50 face the conductive film 33 (bit line BL)and accordingly, the conductive films 43 and are capacitively coupled tothe conductive film 33. Accordingly, when the voltage of the source lineSL is increased, the bit line BL is increased to the voltage value(≈Vera) close to the voltage Vera due to the capacitive coupling. Theconductive film 33 as the bit line BL is electrically connected to thefirst portion (body) 15 a of the pillar 15 through the via 31 and theconductive film 29, and thus the portion of the upper side (selectiongate transistor SDT side) along the z-axis of the body 15 a is increasedto the voltage (≈Vera) close to the voltage Vera due to the increase ofthe voltage of the bit line BL. Thus, the voltage of the body isincreased to the voltage (≈Vera) close to the voltage Vera in itsentirety.

The body 15 a is capacitively coupled to the conductive film 23 (wordline WL and selection gate line SGDL). When the voltage of the body 15 ais increased, the voltages of the selection gate line SGDL and the wordline WL are increased to the voltage (≈Vera) close to the voltage Veraby the capacitive coupling.

The sequencer 141 applies the voltage Vwl to all of the word lines WL ofthe selected block BLK from time t21. The voltage Vwl is higher than thevoltage Vss and is lower than the voltage Vera.

The sequencer 141 makes all the selection gate lines SGSL_0 to SGSL_3into an electrically floating state from time t22. As a result, when thevoltage of the body 15 a is increased, the voltages of the selectiongate lines SGSL_0 to SGSL_3 are increased to the voltage (≈Vera) closeto the voltage Vera due to the capacitive coupling with the body 15 a.

An erasure by drawing out of electrons is performed by the applicationof the voltage in a period of time from time t22 to time t23. That is, alarge potential difference is formed between the body 15 a and the wordline WL in the selected block BLK due to the voltage close to thevoltage Vera and the voltage Vwl. The electrons in the floating gateelectrode film 19 of the selected block BLK are drawn into the body 15 aby the potential difference, and the erasure is performed.

On the other hand, the word line WL is electrically floating in thenon-selected block BLK from time t21. For that reason, when the voltageof the body 15 a is increased due to the capacitive coupling with thebody 15 a, the word line WL is increased to the voltage (≈Vera) close tothe voltage Vera. A potential difference is not formed between the wordline WL and the body 15 a, and the erasure is not performed in thenon-selected block BLK.

The sequencer 141 discharges the CP well 12, the bit line BL, and thesource line SL at time t23. As a result, the voltages, which areincreased due to the coupling, of the selection gate lines SGDL and SGSLof all the strings STR, and all the word lines WL0 to WLn, the bit lineBL, and the source line SL are decreased toward the voltage Vss.

The sequencer 141 discharges the voltage applied to the selected wordlines SGDL and SGSL and the word lines WL0 to WLn of the selected blockBLK to the voltage Vss from time t24 and ends the erasure.

The potentials of several wiring lines between time t21 and time t23 areillustrated in FIG. 21 in a table format.

Advantages (Effects)

According to the fourth embodiment, in the memory device 100 having theshared pillar structure, the voltage Vera is applied to the CP well 12and a voltage, which is the same extent to the voltage Vera, is appliedto the selection gate line SGSL while all of wiring lines of the blockBLK are electrically floating, during erasing. As a result, the voltageof the body 15 a is increased to the voltage value close to the voltageVera through the selection gate transistor SST by a voltage increase ofvarious wiring lines due to the coupling between the selection gatetransistor SST, in which the body 15 a is in the charge accumulationstate, and various wiring lines. In this state, the voltage Vwl isapplied to the word line WL of the selected block BLK. As a result, alarge potential difference is formed between the body 15 a and the wordline WL in the selected block BLK and electrons are drawn into the body15 a, and the erasure is performed. On the other hand, the word line WLis electrically floating and a large potential difference between theword line WL and the body is not formed in the non-selected block BLK,and the erasure is not performed. That is, selective erasure withrespect to the selected block BLK becomes possible.

In the present specification and claims, the term “connection” includesa direct connection and a connection through a conductive element.

In a case where the memory device 100 is a NAND-type flash memory, thememory device 100 may perform the following operations or has thefollowing configuration.

In a multi-level reading operation (read), when the threshold voltagesare set as a level A, a level B, and a level C in ascending order of thethreshold voltage, a voltage to be applied to a selected word line for alevel A reading operation is, for example, in a range of 0 V to 0.55 V.The voltage is not limited thereto and may include any range of 0.1 V to0.24 V, of 0.21 V to 0.31 V, of 0.31 V to 0.4 V, of 0.4 V to 0.5 V, of0.5 V to 0.55 V, and the like. A voltage to be applied to a selectedword line for a level B reading operation is, for example, of 1.5 V to2.3 V. The voltage is not limited thereto and may include any range of1.65 V to 1.8 V, of 1.8 V to 1.95 V, of 1.95 V to 2.1 V, of 2.1 V to 2.3V, and the like. A voltage to be applied to a selected word line for alevel C reading operation is, for example, of 3.0 V to 4.0 V. Thevoltage is not limited thereto and may include any range of 3.0 V to 3.2V, of 3.2 V to 3.4 V, of 3.4 V to 3.5 V, of 3.5 V to 3.6 V, of 3.6 V to4.0 V, and the like. A reading operation time (tR) may be, for example,any range of 25 μs and 38 μs, of 38 μs and 70 μs, of 70 μs and 80 μs,and the like.

The writing operation includes a program operation and a verificationoperation. In the writing operation, a voltage applied to the selectedword line during the program operation for the first time is, forexample, a range of 13.7 V to 14.3 V. The voltage is not limited theretoand may include, for example, any range of 13.7 V to 14.0 V, of 14.0 Vto 14.6 V, and the like. The voltage applied to the selected word linefor the first time when writing an odd-numbered word line may differfrom the voltage applied to the selected word line for the first timewhen writing an even-numbered word line. When an incremental step pulseprogram (ISPP) is used for the program operation, a step-up voltage maybe, for example, approximately 0.5 V. The voltage to be applied to thenon-selected word line may be, for example, a range of 6.0 V to 7.3 V.The voltage is not limited thereto and may be in a range, for example,of 7.3 V to 8.4 V, and may be 6.0 V or less. A pass voltage to beapplied may differ depending on whether the non-selected word line iseither an odd-numbered word line or an even-numbered word line. Thewriting operation time (tProg) may be in a range, for example, of 1000μs to 1500 μs, of 1500 μs to 2000 μs, and of 2000 μs to 3000 μs.

In the erasing operation, a voltage applied to a well, which is disposedat the upper part of a semiconductor substrate and above a memory cell,for the first time is in a range, for example, of 12 V to 13.6 V. Thevoltage is not limited thereto and may be in any range, for example, of13.6 V to 14.8 V, of 14.8 V to 19.0 V, of 19.0 V to 19.8 V, and of 19.8V to 21 V. The erasing operation time (tErase) may be in a range, forexample, of 1000 μs to 3000 μs, of 3000 μs to 5000 μs, and of 5000 μs of10000 μs.

The memory cell may have a structure as described in the following, forexample. The memory cell includes a charge accumulation layer disposedon a semiconductor substrate, such as a silicon substrate, through atunnel insulating film having a film thickness of 4 nm to 10 nm. Thecharge accumulation layer may be configured in a stacked structure of aninsulating film such as a silicon oxide (SiON) film or a silicon nitride(SiN) film having a film thickness of 3 nm to 8 nm and a poly-silicon(Poly-Si) film having a film thickness of 3 nm to 100 nm. A metal suchas ruthenium (Ru) may be added to a portion of the charge accumulationlayer. An insulating film may be formed on the charge accumulationlayer. The insulating film includes a High-k film having a filmthickness of 4 nm to 10 nm which is sandwiched by, for example, alower-layer silicon oxide (SiO₂) film having a film thickness of 3 nm to10 nm and an upper-layer silicon oxide film having a film thickness of 3nm to 10 nm. Materials of the High-k film may include hafnium oxide(HfO) or the like. The film thickness of the silicon oxide film may begreater than that of the High-k film. A control electrode having a filmthickness of 30 nm to 100 nm is provided on the insulating film througha film having a thickness of 1 nm to 10 nm. Such a film includes, forexample, a metal oxide film such as tantalum oxide (TaO), a metal oxidefilm or a metal nitride film such as tantalum nitride (TaN), tungstennitride (WN), or aluminum oxide (AlO). Tungsten (W) may be used in thecontrol electrode. An air gap may be provided between the memory cells.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A memory device comprising: a semiconductorcolumn extending above a substrate; a first conductive layer on a firstside of the semiconductor column; a second conductive layer on a secondside of the semiconductor column, opposite to the first conductivelayer; a third conductive layer above or below the first conductivelayer and on the first side of the semiconductor column; a fourthconductive layer on the second side of the semiconductor column,opposite to the third conductive layer; a fifth conductive layeradjacent the first conductive layer on the first side of thesemiconductor column and between the first and third conductive layers;a sixth conductive layer on the second side of the semiconductor column,opposite to the fifth conductive layer; and a bit line connected to thesemiconductor column, wherein during reading in which a positive voltageis applied to the bit line: a first voltage is applied to the firstconductive layer and a second voltage is applied to the secondconductive layer; a third voltage is applied to the third conductivelayer and a fourth voltage is applied to the fourth conductive layer; afifth voltage is applied to the fifth conductive layer and a sixthvoltage is applied to the sixth conductive layer; the first voltage andthe third voltage are higher than each of the second voltage and thesixth voltage; the fifth voltage is higher than the first, second,third, fourth and sixth voltages; and the third voltage is higher thanthe first voltage.
 2. The memory device according to claim 1, whereinthe second, fourth, and sixth voltages are negative voltages.
 3. Thememory device according to claim 1, wherein the second and fourthvoltages are negative voltages, and the sixth voltage is a positivevoltage.
 4. The memory device according to claim 1, wherein thesemiconductor column has a first pillar portion that faces the first andthird conductive layers and extends above the substrate, and a secondpillar portion that faces the second and fourth conductive layers andextends above the substrate, the first and second pillar portions beingelectrically isolated from each other.
 5. The memory device according toclaim 4, further comprising: a first transistor that controls anelectrical connection and disconnection between the bit line and thefirst pillar portion; and a second transistor that controls anelectrical connection and disconnection between the bit line and thesecond pillar portion, wherein during the reading in which the positivevoltage is applied to the bit line, the first transistor is turned onand the second transistor is turned off.
 6. The memory device accordingto claim 1, further comprising: a second semiconductor column extendingabove the substrate and connected to the bit line, wherein the first andthird conductive layers extend parallel to a surface of the substrate toface a first side of the second semiconductor column.
 7. The memorydevice according to claim 6, further comprising: seventh and eighthconductive layers on a second side of the second semiconductor column,opposite to the first and third conductive layers, respectively.
 8. Thememory device according to claim 7, wherein during the reading in whichthe positive voltage is applied to the bit line, negative voltages areapplied to the seventh and eighth conductive layers.
 9. The memorydevice according to claim 7, wherein during the reading in which thepositive voltage is applied to the bit line, a negative voltage is tothe seventh conductive layer and a positive voltage less than the firstvoltage is applied to the eighth conductive layer.